add: initial implementation of unit test for pdf export

Author: bradjin8

tests/test_pdf_export.py

@@ -0,0 +1,99 @@
+"""Unit tests for POST /api/generate-pdf (api/pdf.py)."""
+
+from __future__ import annotations
+
+from unittest.mock import patch
+
+PDF_MAGIC = b"%PDF-"
+
+
+def _post_pdf(client, *, markdown: str = "", title: str = "Chat", json_data=None):
+    if json_data is not None:
+        return client.post(
+            "/api/generate-pdf",
+            json=json_data,
+            content_type="application/json",
+        )
+    return client.post(
+        "/api/generate-pdf",
+        json={"markdown": markdown, "title": title},
+        content_type="application/json",
+    )
+
+
+def _assert_pdf_response(response) -> None:
+    assert response.status_code == 200
+    assert response.content_type.startswith("application/pdf")
+    data = response.data
+    assert len(data) > 0
+    assert data.startswith(PDF_MAGIC)
+    # Trailing %%EOF is a minimal structural check (see tests/web-ui-qa-checklist.md).
+    assert b"%%EOF" in data[-1024:]
+
+
+class TestGeneratePdfHappyPath:
+    def test_normal_conversation_markdown(self, client):
+        md = """# Chat export
+
+## User question
+
+Please explain **recursion** in Python.
+
+- Base case
+- Recursive step
+
+```python
+def fact(n):
+    return 1 if n < 2 else n * fact(n - 1)
+```
+
+---
+"""
+        response = _post_pdf(client, markdown=md, title="Happy conversation")
+        _assert_pdf_response(response)
+        assert (
+            'attachment; filename="Happy conversation.pdf"'
+            in response.headers.get("Content-Disposition", "")
+        )
+
+
+class TestGeneratePdfEdgeCases:
+    def test_empty_markdown(self, client):
+        response = _post_pdf(client, markdown="", title="Empty chat")
+        _assert_pdf_response(response)
+
+    def test_very_long_content(self, client):
+        line = "This is a repeated paragraph for length testing. " * 20
+        md = "\n".join(f"Line {i}: {line}" for i in range(500))
+        response = _post_pdf(client, markdown=md, title="Long chat")
+        _assert_pdf_response(response)
+
+    def test_unicode_and_emoji_content(self, client):
+        md = (
+            "Smart quotes: “hello” and ’world’\n"
+            "Emoji: 🚀🔥 should not break PDF\n"
+            "Bullet • point\n"
+        )
+        response = _post_pdf(client, markdown=md, title="Unicode chat")
+        _assert_pdf_response(response)
+
+
+class TestGeneratePdfErrors:
+    def test_pdf_engine_failure_returns_500(self, client):
+        with patch(
+            "fpdf.fpdf.FPDF.output",
+            side_effect=RuntimeError("simulated failure"),
+        ):
+            response = _post_pdf(client, markdown="Hello", title="Fail")
+        assert response.status_code == 500
+        assert response.get_json() == {"error": "Failed to generate PDF"}
+
+    def test_invalid_export_payload_returns_500(self, client):
+        # Conversation IDs are resolved client-side (tabs API) before markdown is
+        # POSTed here. A non-string markdown field mimics a corrupted export request.
+        response = _post_pdf(
+            client,
+            json_data={"markdown": ["not", "a", "string"], "title": "Bad payload"},
+        )
+        assert response.status_code == 500
+        assert response.get_json() == {"error": "Failed to generate PDF"}